1. Field of the Invention
The present invention relates to a communication terminal apparatus such as a mobile station communication apparatus used for digital radio communications, base station communication apparatus and radio communication method.
2. Description of the Related Art
A multiple access system is used as a circuit-switching system when a plurality of stations carry out communications using a same band simultaneously in the digital radio communication field, and TDMA (Time Division Multiple Access) and CDMA (Code Division Multiple Access), etc. are examples of this. TDMA refers to Time Division Multiple Access, a multiple access technology that compresses an information signal on the time scale and carries out transmission/reception within an assigned time slot. On the other hand, CDMA refers to Code Division Multiple Access, a technology that implements multiple access through a spread spectrum communication that transmits an information signal by spreading its spectrum over a frequency band wide enough compared to the original information bandwidth. Here, a direct spreading system is a system that carries a sequence of spreading codes on an information signal as they are by spreading.
On the other hand, radio communication technologies conventionally use duplex systems such as FDD (Frequency Division Duplex) system and TDD (Time Division Duplex) system for the purpose of improving the communication efficiency. For example, TDD refers to a system using a same band for transmission/reception, and is also called a xe2x80x9cping-pong systemxe2x80x9d which carries out communications by time-sharing a same radio frequency for transmission and reception. Since the TDD system does not require an uplink/downlink pair band, it can be used not only for public services but also for local area or home services in many cases. The TDD system also has an advantage of its ability to facilitate asymmetric transmission rate services by flexibly handling differences in uplink/downlink traffic or services.
Some applications combine a multiple access communication system such as a TDMA or CDMA system above with an FDD or TDD communication system. A CDMA/TDD system in particular can efficiently increase the number of channels accommodated and is expected to be used widely in the future.
In the case of the CDMA/TDD system, transmitting data over one entire frame using different spreading codes for the uplink and downlink is believed to suppress the level of interference between systems as described in ARIB Volume 3 xe2x80x9cSpecifications of Air-Interface for 3G Mobile System (Ver.0.5).
Information specific to a base station apparatus such as downlink transmission power or uplink interference power is also transmitted over one entire frame via a spread broadcast channel (BCCH). However, if base station communication apparatuses come quite closer to each other, the amount of interference power increases even if different spreading codes are used, which may deteriorate the system characteristics.
FIG. 1 shows a downlink frame structure when a conventional CDMA/TDD system is introduced to home services and services symmetric between the uplink and downlink are carried out. As seen from FIG. 1, a communication channel and broadcast channel are split into a plurality of downlink slots and information to be transmitted is transmitted over one entire frame.
On the other hand, recent progress in the cellular system technology has made it possible to develop a self-operated (home-based) system that carries out communications by freely selecting the uplink and downlink locations of time slots in a signal frame. In this case, it is also important to consider common factors between a public service and home service. However, conventional systems are not applicable to such a self-operated system at all.
In FIG. 1, the broadcast channels in four systems use common slots, but the level of interference increases as the number of systems operating in the same area increases.
It is an objective of the present invention to provide a communication terminal apparatus, base station communication apparatus and radio communication method capable of suppressing interference between systems and commonly applicable to public and home services.
A main point of the present invention is to flexibly handle various services and avoid the problem of interference in self-operated services in particular by using signals having a TDMA structure in the CDMA/TDD system and carrying out transmission/reception of broadcast channels only with the last downlink slot of a subframe.
Another main point of the present invention is to make the most of features of uplink open-loop transmission power control and base station transmission diversity by a base station communication apparatus repeatedly transmitting information contained in broadcast channels by a number of times corresponding to the time-sharing number and allotting an appropriate number of slots for the uplink and downlink.